A 35-year-old male having sex with men (MSN) reported about recurrent anal pain, haematochezia and mild diarrhoea. Colonoscopy showed proctitis with edematous and erythematous rectal mucosa and a circumscribed ulcer right above the anal canal. Biopsies were taken. Clinical differential diagnosis: ulcerative proctitis versus infectious proctitis.
Histological examination disclosed chronically inflamed large bowel mucosa with ulcer and fragments of granulation tissue (Panel A). In the preserved parts of the mucosa, there was mild crypt architectural distortion with occasional branching of crypts, but no prominent crypt irregularities or crypt atrophy (Panel B). The lamina propria contained a dense lymphoplasmacytic infiltrate which extended into the submucosa; few neutrophils and occasional active crypt inflammation / cryptitis were present (Panel C). Deep within the lamina propria an ill-defined non-necrotic granuloma was detected that consisted of a loose collection of epithelioid histiocytes (Panels D-E).
The histological findings were consistent with infectious proctitis, particularly with a sexually transmitted infection (STI). The deep and plasma cell-rich inflammatory infiltrate together with the occurrence of a granuloma indicated Lymphogranuloma Venereum (LGV) which is caused by infection with Chlamydia trachomatis serotypes L1, L2 and L3. Upon request by the clinicians, DNA was extracted from the FFPE biopsy samples and a real-time PCR assay was performed that confirmed presence of Chlamydia trachomatis specific DNA.
STI proctocolitis is underrecognized by clinicians and pathologists due to lacking awareness of the disease and its clinical and histological characteristics. It is often misdiagnosed as inflammatory bowel disease, but there are histopathological features that can help to distinguish STI proctocolitis from IBD. In contrast to IBD, STI proctocolitis is usually lacking prominent crypt architectural distortion, basal plasmacytosis and mucosal eosinophilia. In addition, crypt centered active inflammation (cryptitis, crypt abscesses) is much less pronounced compared to ulcerative proctocolitis and Crohn’s disease. By being familiar with the histopathogical pattern of STI proctocolitis, pathologists can contribute to timely and correct treatment and help to avoid patient mismanagement and STI transmission.
